The present invention relates to improvements of a mechanical technique for a robot arm and a control technique for a robot arm, and also relates to a robot, a control device for a robot arm, and a control program for a robot arm.
In recent years, developments of home-use robots such as pet robots have been vigorously carried out, and it is expected that in the future, more practical home-use robots, such as house-keeping support robots or the like, will be put into practical use. Since the home-use robots need to enter the home and coexist with human beings, the robots are inevitably physically made in contact with the human beings so that they need to be flexible from the viewpoint of safety.
Moreover, in factories, an attempt has been made to automate an assembling task, a recycling scrapping task or the like; however, in the case where the contents of the task are complicated or there are various environments, such as a state in which the use of a jig is difficult because of a small quantity of products with a large number of product types, and the position of the corresponding part is indefinite, conventional industrial robots fails to provide a sufficient solution.
In contrast, there is proposed a task assistant robot in which the human being mainly carries out a task, while the robot assists the human being, so that the efficiency of the task is improved. Since the robot that assists the human being is operated near a person, it needs to be flexible from the viewpoint of safety.
As a flexible robot, a pneumatic arm that uses a pneumatic actuator as a driving device has been developed. The pneumatic arm, which utilizes a compressive characteristic of air, has flexibility from a mechanical point of view, and is originally safe in comparison with a system that provides flexibility from the controlling motions.
However, the pneumatic arm tends to easily cause vibrations because of its flexibility, and makes it difficult to provide high precision in determining the position of the arm-end upon carrying out a high-speed motion, and in particular, makes it difficult to be applied to a task required for high precision, such as an assembling task in a factory.
In the attempt to improve the position-determining precision of the arm-end, as a related art, Patent Document 1 proposes a technique in which, as shown in FIG. 27, an end effector 201, provided with position and orientation guides 204a, 204b, and 204c having flexibility, is attached to the arm-end of the robot arm (not shown) so that the part is held by the end effector 201, while the position of the target object is detected, with the part and the target object being held in a non-contact state, and the center axes thereof are made coincident with each other; thus, engaging processes or screw-tightening processes are carried out with high controllability.
Moreover, Patent Document 2 proposes a technique in which at least two joints on the base end side are prepared as flexible movable joints, and by placing an elbow frame on a table, the position or orientation of a hand can be ensured with high precision.
Furthermore, Patent Document 3 proposes a technique in which, by making an end effector in contact with a desired task in a force control mode, a precise positioning process is carried out so that positional data can be obtained.
Patent Document 1: Japanese Unexamined Patent Publication No. H5-84685
Patent Document 2: Japanese Unexamined Patent Publication No. 2009-125886
Patent Document 3: Japanese Unexamined Patent Publication No. H5-329787
However, the structure of Patent Document 1 fails to exert its effects, unless the target object is a convex-shaped object, such as a bolt, that can be enclosed by position and orientation guides 204a, 204b, and 204c, and the technique is specialized to a specific task, for example, failing to deal with a screw that is inserted into a counter sunk hole, and is not applicable to a general technique for use in improving the position-determining precision of a flexible robot arm, such as a pneumatic arm.
Moreover, the structure of Patent Document 2 can improve the precision of the arm-end position and orientation by placing the robot arm elbow on the table so that the robot arm is stabilized; however, this technique fails to be applied as a technique for use in improving the precision at high-speed motions, such as motions in which, after the arm-end has been shifted at a high speed, a decelerating process is abruptly carried out to conduct a positioning process.
Since the structure of Patent Document 3 carries out a force controlling motion with the end effector being made in contact with a work, this is not used as a technique by which, with an object being grabbed, a task is carried out by changing the position or orientation of the object.
In view of the above conventional issues, an object of the present invention is to provide a robot that is flexible with high safety, and can control the position and orientation of an end effector or a grabbed object with high precision, even in the case of a high-speed motion, a control device for a robot arm, and a control program for the robot arm.